1. Field of the Disclosure
The present disclosure relates to a synchronous switching control method of a medium voltage inverter.
2. Discussion of the Related Art
In a medium voltage inverter, electrical impacts by various causes are applied to a motor, an inverter, and a commercial power source, during the switching action between an inverter output power source and a commercial power source.
The electrical impact is generated by the instantaneous intermittence section which is generated in a section which the switches of the commercial power source and the inverter are both opened during the switching action. In order to reduce the electrical impact caused by the voltage generated while the voltage inputted to the motor is switched from the invert output to the commercial power source, the magnitude and phase of the inverter output and the commercial power source should be adjusted as identical to each other.
FIG. 1 is an exemplary view illustrating synchronous switching of a conventional medium voltage inverter.
In a conventional medium voltage inverter system, an output voltage is measured at a back end of the reactor, and the medium voltage inverter (100) compensates the phase delay of the voltage generated by the reactor. As such, when the switching operation is made after the commercial power source and the inverter output voltage are in synchronization, the electrical impacts generated by the voltage difference may be considerably reduced.
However, because the conventional medium inverter synchronous switching as illustrated in FIG. 1 is to control ON or OFF of switches in a situation where the high-voltage power source is applied, the malfunction of switching operation may lead to a high-voltage accident.
In addition, when the switch of the commercial power source is maintained in a ON status while the medium inverter is driving the motor, both of the power sources are applied to both ends of the reactor, and then a current is generated by the voltage difference between both of the power sources, which may lead to an accident in the medium voltage inverter and the commercial power source. And in the situation where a large amount of current is flowing due to a large voltage difference, there may be generated problems such as overcurrent cutoff of the commercial power source, overcurrent malfunction of the medium voltage inverter, etc.